During operation, the individual blades of a turbomachine execute natural frequency vibrations which depend on the type of vibration to which they are subjected-tangential bending, axial bending or torsion. If several blades are connected together to form a group, by means of bandaging, for example, the behaviour of the blades becomes still more complex because each type of vibration has to have allocated to it as many natural frequencies as there are blades in a group. Because of the large number of natural frequencies, it is very difficult to avoid resonance phenomena with periodic excitation forces.
In contrast, continuous connection of all the rotor blades in a wheel leads to completely different behaviour. Since only coupled vibrations of all the blades are possible, the excitation forces must be in phase with the type of vibration over the complete periphery of the wheel if a transfer of energy to the blades is to take place at all. This type of blade connection is particularly useful for the control stage of a turbine whose rotor blades are made to vibrate by periodic forces originating from the vane segments of the first guide vane stage, the nozzle box, and whose frequencies represent a multiple of the frequency of rotation.
A rotor blade ring of the type mentioned at the beginning is known, for example, from the book "Thermische Turbomaschinen" by Walter Traupel, 3rd edition, second volume, Figure 20.21.3 and the associated description. The solution mentioned, i.e. connecting wires caulked into the shroud plates, is referred to as a "design well worth noting".
However, it has been found that frettage corrosion due to vibration occurs at the locations at which the wire penetrates the end surfaces of the shroud plates and this can lead to failure of the wire.